Question

Find the sum of first 20 term of the AP 5,11,17, ...​

Answer 1

Answer:

• 1240 is the sum of the first 20 terms.

Step-by-step explanation:

Given :

$\bold{A.P:5,11,17..}$

To find :

$\bold{Sum\;of\;first\;20\;terms\;of\;the\;A.P.}$

Solution :

We have:

$\rightarrow \bold{First\;term(a)=5}$

$\rightarrow \bold{Common \;difference(d)=11-5=6}$

We know:

$\rightarrow \bold{S_n=\dfrac{n}{2}(2a+(n-1)d) }$

Hence:

$\rightarrow \bold{20 = \dfrac{20}{2}[2(5)+(20-1)6 ]}$

$\rightarrow \bold{20=10(10+(19)6)}$

$\rightarrow \bold{20=10(10+114)}$

$\Rightarrow \bold{S_{20}=1240}$

∴ $\bold{Sum\;of\;first\;20\;terms\;of\;the\;given\;A.P\;is\;1240.}$

Answer 2

Answer:

check this out

Step-by-step explanation:

hope it helps you